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Date: Thu, 18 Jun 2015 12:27:12 -0700 (PDT)
From: David Rientjes <rientjes@...gle.com>
To: Michal Hocko <mhocko@...e.cz>
cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] oom: split out forced OOM killer
On Thu, 18 Jun 2015, Michal Hocko wrote:
> The forced OOM killing is currently wired into out_of_memory() call
> even though their objective is different which makes the code ugly
> and harder to follow. Generic out_of_memory path has to deal with
> configuration settings and heuristics which are completely irrelevant
> to the forced OOM killer (e.g. sysctl_oom_kill_allocating_task or
> OOM killer prevention for already dying tasks). All of them are
> either relying on explicit force_kill check or indirectly by checking
> current->mm which is always NULL for sysrq+f. This is not nice, hard
> to follow and error prone.
>
> Let's pull forced OOM killer code out into a separate function
> (force_out_of_memory) which is really trivial now.
> As a bonus we can clearly state that this is a forced OOM killer
> in the OOM message which is helpful to distinguish it from the
> regular OOM killer.
>
Ok, so this patch reverts _everything_ in the first patch other than the
documentation. Just start with this patch instead, sheesh.
> Signed-off-by: Michal Hocko <mhocko@...e.cz>
> ---
> drivers/tty/sysrq.c | 3 +--
> include/linux/oom.h | 3 ++-
> mm/oom_kill.c | 57 ++++++++++++++++++++++++++++++++---------------------
> mm/page_alloc.c | 2 +-
> 4 files changed, 39 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> index 3a42b7187b8e..06a95a8ed701 100644
> --- a/drivers/tty/sysrq.c
> +++ b/drivers/tty/sysrq.c
> @@ -356,8 +356,7 @@ static struct sysrq_key_op sysrq_term_op = {
> static void moom_callback(struct work_struct *ignored)
> {
> mutex_lock(&oom_lock);
> - if (!out_of_memory(node_zonelist(first_memory_node, GFP_KERNEL),
> - GFP_KERNEL, 0, NULL, true))
> + if (!force_out_of_memory())
> pr_info("OOM request ignored because killer is disabled\n");
> mutex_unlock(&oom_lock);
> }
> diff --git a/include/linux/oom.h b/include/linux/oom.h
> index 7deecb7bca5e..061e0ffd3493 100644
> --- a/include/linux/oom.h
> +++ b/include/linux/oom.h
> @@ -70,8 +70,9 @@ extern enum oom_scan_t oom_scan_process_thread(struct task_struct *task,
> unsigned long totalpages, const nodemask_t *nodemask,
> bool force_kill);
>
> +extern bool force_out_of_memory(void);
> extern bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> - int order, nodemask_t *mask, bool force_kill);
> + int order, nodemask_t *mask);
>
> extern void exit_oom_victim(void);
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 0c312eaac834..050936f35944 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -635,12 +635,38 @@ int unregister_oom_notifier(struct notifier_block *nb)
> EXPORT_SYMBOL_GPL(unregister_oom_notifier);
>
> /**
> - * __out_of_memory - kill the "best" process when we run out of memory
> + * force_out_of_memory - forces OOM killer
... to kill a process.
> + *
> + * External trigger for the OOM killer. The system doesn't have to be under
> + * OOM condition (e.g. sysrq+f).
> + */
I'm still not sure what you mean by external. I assume you're referring
to induced by userspace rather than the kernel. I think you should use
the word "explicit".
> +bool force_out_of_memory(void)
> +{
> + struct zonelist *zonelist = node_zonelist(first_memory_node, GFP_KERNEL);
> + struct task_struct *p;
> + unsigned long totalpages;
> + unsigned int points;
> +
> + if (oom_killer_disabled)
> + return false;
> +
> + constrained_alloc(zonelist, GFP_KERNEL, NULL, &totalpages);
> + p = select_bad_process(&points, totalpages, NULL, true);
> + if (p != (void *)-1UL)
> + oom_kill_process(p, GFP_KERNEL, 0, points, totalpages, NULL,
> + NULL, "Forced out of memory killer");
> + else
> + pr_warn("Forced out of memory. No killable task found...\n");
Please consider the review from the first patch about this line.
> +
> + return true;
> +}
> +
> +/**
> + * out_of_memory - kill the "best" process when we run out of memory
> * @zonelist: zonelist pointer
> * @gfp_mask: memory allocation flags
> * @order: amount of memory being requested as a power of 2
> * @nodemask: nodemask passed to page allocator
> - * @force_kill: true if a task must be killed, even if others are exiting
> *
> * If we run out of memory, we have the choice between either
> * killing a random task (bad), letting the system crash (worse)
> @@ -648,7 +674,7 @@ EXPORT_SYMBOL_GPL(unregister_oom_notifier);
> * don't have to be perfect here, we just have to be good.
> */
> bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> - int order, nodemask_t *nodemask, bool force_kill)
> + int order, nodemask_t *nodemask)
> {
> const nodemask_t *mpol_mask;
> struct task_struct *p;
> @@ -687,14 +713,8 @@ bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> constraint = constrained_alloc(zonelist, gfp_mask, nodemask,
> &totalpages);
> mpol_mask = (constraint == CONSTRAINT_MEMORY_POLICY) ? nodemask : NULL;
> - /* Ignore panic_on_oom when the OOM killer is sysrq triggered */
> - if (!force_kill)
> - check_panic_on_oom(constraint, gfp_mask, order, mpol_mask, NULL);
> + check_panic_on_oom(constraint, gfp_mask, order, mpol_mask, NULL);
>
> - /*
> - * not affecting force_kill because sysrq triggered OOM killer runs from
> - * the workqueue context so current->mm will be NULL
> - */
> if (sysctl_oom_kill_allocating_task && current->mm &&
> !oom_unkillable_task(current, NULL, nodemask) &&
> current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
> @@ -705,18 +725,11 @@ bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> goto out;
> }
>
> - p = select_bad_process(&points, totalpages, mpol_mask, force_kill);
> - /*
> - * Found nothing?!?! Either we hang forever, or we panic.
> - * Do not panic when the OOM killer is sysrq triggered.
> - */
> + p = select_bad_process(&points, totalpages, mpol_mask, false);
> + /* Found nothing?!?! Either we hang forever, or we panic. */
> if (!p) {
> - if (!force_kill) {
> - dump_header(NULL, gfp_mask, order, NULL, mpol_mask);
> - panic("Out of memory and no killable processes...\n");
> - } else {
> - pr_info("Forced out of memory. No killable task found...\n");
> - }
> + dump_header(NULL, gfp_mask, order, NULL, mpol_mask);
> + panic("Out of memory and no killable processes...\n");
> }
> if (p != (void *)-1UL) {
> oom_kill_process(p, gfp_mask, order, points, totalpages, NULL,
> @@ -747,7 +760,7 @@ void pagefault_out_of_memory(void)
> if (!mutex_trylock(&oom_lock))
> return;
>
> - if (!out_of_memory(NULL, 0, 0, NULL, false)) {
> + if (!out_of_memory(NULL, 0, 0, NULL)) {
> /*
> * There shouldn't be any user tasks runnable while the
> * OOM killer is disabled, so the current task has to
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 1f9ffbb087cb..014806d13138 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2731,7 +2731,7 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
> goto out;
> }
> /* Exhausted what can be done so it's blamo time */
> - if (out_of_memory(ac->zonelist, gfp_mask, order, ac->nodemask, false)
> + if (out_of_memory(ac->zonelist, gfp_mask, order, ac->nodemask)
> || WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL))
> *did_some_progress = 1;
> out:
--
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